The opioid-receptor-like (ORL1) receptor, like the classical mu, delta, and kappa opioid receptors, belongs to the G protein-coupled, seven-transmembrane receptor superfamily. Binding of its endogenous peptide ligand nociceptin/orphanin FQ (NOC/OFQ) to ORL1 initiates a G protein-mediated signal transduction pathway, which fulfills essential functions in regulation of nociception, long-term potentiation and response to stress. ORL1 is expressed in multiple alternative splicing forms in a tissue-, cell-type-, and development-specific manner. However, the molecular mechanisms underlying the regulation of the spatially and temporally differential expression of ORL1 are poorly understood and have not been thoroughly investigated. Furthermore, regulators of G protein signaling (RGS) are now believed to play a crucial role in opioid recetor/G protein-mediated signaling. The role of RGS proteins in ORL1 signal transduction is a main focus of this grant. The discovery by this laboratory that the human ORL1 and GAIP (G alpha interacting protein, also named RGS19) genes are linked and their transcriptions are controlled by a shared bi-directional promoter, as well as the new finding that an activation of ORL1 by NOC/OFQ up-regulates GAIP transcription and that GAIP negatively regulates ORL1 signal transduction, have suggested a significant functional role of GAIP in regulating ORL1 gene expression and function. [unreadable] The tight linkage of ORL1 and GAIP genes provides a unique basis to study the transcription regulation of ORL1 and GAIP, and to study the functional role of GAIP and other RGSs in ORL1 signaling. This grant application proposes a hypothesis that GAIP not only physically couples to the ORL1 gene, but also plays a crucial role in regulating ORL1 gene expression and signal transduction. To examine the hypothesis and establish the functional role of GAIP in regulating ORL1, this application proposes specific aims to investigate how ORL1 specifically regulates GAIP transcription and activity, and in turn, how GAIP can specifically modulate ORL1 expression and function. This application also proposes to examine the selectivity of GAIP in regulating ORL1 signaling by comparing with other RGS proteins. Finally, this study also aims to further analyze the functional activities of the key promoter regions of ORL1 and GAIP genes, hence further exploring the mechanisms that control the coordinated but differential cell-type-specific expression of ORL1 and GAIP genes and their alternative splicing variants. This proposed research will help us to understand the regulatory role of GAIP and RGSs in ORL1 signal transduction and gene expression, lay the basis for a novel strategy of modulating NOC/OFQ and ORL1 functions by manipulating GAIP (RGS) gene expression and activity, and therefore, may provide strategic targets for therapeutic applications in pain management and other neurological and mental disorders related to the ORL1 system. [unreadable] [unreadable]